Chapter 11- Fish and mammals

Chapter 11- Fish and mammals• Zebrafish are becoming the sweetheart of developmental

biologists

Fig. 11.1

• Large broods• Breed year-round• Easy and cheap• Transparent embryos• Develop outside mother• Early development complete in 24 hours

1

6

Blastoderm is perched on a

large ________

1st 12 divisions are sychronous to form _____________

3. ____________ layer (YSL)

Three cell populations1. __________

_____ (EL)

2. ____layer- gives rise to embryo proper

Fig. 11.2

A. Cleavage

Fig. 11.3

B. Gastrulation

EpibolyDeep cells migrate to outside then encase entire yolk

Movement not by crawling, but by YSL cells expansion and pulling EL cells along

• A ________ is formed either by _________ of superficial cells or by _______• These combine with superficial epiblast cells to form the _______________ (function equivalent of the dorsal lip in amphibians)

1. Enveloping layer (EL)

2. Deep cells

3. YSL cells

hypoblast

epiblastEmbryonic shield

6 hrs post-fertilization

YSL

Recall Epiboly from Ch 9

Fig. 11.3

B. Gastrulation (cont.)

The hypoblast cells extend in both directions to form the notochord precursor

Animal

Vegetal

Ventral Dorsal

Head

TailTrunk

Fig. 11.2 -A zebrafish fate map

Ectoderm

Mesoderm

Endoderm

C. Axis formation1. Dorsal ventral axis-

1. Establishes the _______________ axis• Converts lateral/ventral medoderm to

dorsal mesoderm (notochord)• Convert ectoderm to neural rather

than epidermal

2. Forms the ______________ precursor

As with the amphibian __________ (Organizer), the embryonic shield:

B-catenin

samois

goosecoid

BMP inhibitors

e.g. Chordino

C. Axis formation

Fig. 11.6

1. Dorsal ventral axis-

As with the amphibian dorsal lip (Organizer), the embryonic shield:

4. Acquires its function from _________ accumulation in nearby cells

•B-catenin accumulates in _____ cells •______________is activated

BMP2

3. Secretes proteins to inhibit BMP from inducing ectoderm to become epidermis

•This inhibiting molecule is called ___________• If mutate ________, no neural tube is formed

Chordino

Embryonic shield

B-catenin

samois

goosecoid

BMP inhibitors

e.g. Chordino

C. Axis formation (cont.)

Fig. 11.6

3. ________________ axis -

In amphibians , the anterior-posterior axis is formed during oogenesisThis axis is stabilized during gastrulation by _____________ ________________________.

_________ neural inducing signal (from ectoderm cells)

__________ neural-inducing signal ( from mesoderm cells)

2. _________________ axis-

Not much known, but involves ______ family signaling molecules

Mammalian Development

• ______ diameter (1/1000th volume of frog egg!)• Few in number ___________• Develops within mother• Cleavage events take _____ hours each• Development occurs en route to ___________

Tough to study!!

1. Egg released from _____

2. fertilization

3. Cleavage during migration down _________

4. Implant in ______

Fig. 11.20

Mammalian Development

1. Slow- ______ hrs per cleavage2. 2nd cleavage is ______________3. Marked __________ in early cell

division4. Cleavage at 2nd division requires

newly made ________ from zygote

Distinctions of mammalian cleavage

Fig. 11.21-rotational cleavage in mammals

Fig. 11.23- Compaction at 8 cell stage (______ in humans)compaction

5. ____________ (marked cell huddling) occurs at 8 cell stage

A. Cleavage

Amphibians Mammals

16 cell embryo is termed “_______”

•external cells will become ___________, which will become the _________•Internal cells will become _____________ (ICM), or the ______________

A. Cleavage (cont.)

This marks 1st differentiation event in mammalian development

At 64 cell stage, an internal cavity appears and the embryo is termed a ___________, ready for implantation onto uterus wall

The ______________ (recall ch. 7) must be shed in order to implant• Blastocyst ____ a small hole in zona using the enzyme _______

Note- attachment of embryo to oviduct wall is called a ______________.

Similar to __________ and birds

•Mammalian embryo relies on __________ for nutrients, not yolk•Thus, the embryo must have a specialized organ to accept nutrients- called the ___________•The chorion induces uterine cells to become a _________ (rich in blood vessels)

B. Gastrulation

Fig. 11.28- Day 15 human embryo

Hypoblasts (from ICM) line the ________- these give rise to ______________________.

Epiblasts form ______________

blastocoel

hypoblasts

epiblasts

Mammalian ______ and ______ cells arise from epiblasts that migrate through primitive streak

E-cadherin attachment is mechanism

Fig.11.11- Chick gastrulation- similar to mammalian

Fig. 11.28- Day 16 in human

_____________ _____________

Those cells that migrate through the ____________ will become the _________________.

B. Gastrulation (cont.)

Direction of migration

Extraembryonic membrane FormationTrophoblast cells (originally termed “cytotrophoblast”) gives rise to multinucleated ____________________

These syncytiotrophoblasts: • secrete proteolytic enzyme to invade

__________________• Digest uterine tissueMothers blood vessels contact the

syncytiotrophoblast cellsEmbryo produces its own blood vessels

Uterine wall

Fig. 11.27-Blastocyst invading uterus

Blood vessels feed embryo, but blood cells do not mix

Mothers blood vessels

Embryo chorion

Mother’s Placenta

Chorion Villi

Embryo’s blood vessels

Fig. 11.31

B. Gastrulation (cont.)

C. Anterior-posterior axis formation

Two signaling centers1. _______________________ (AVE)2. _________ (Organizer)

Fig. 11.34 These are on opposite sides of a “cup” structure

These work together to form

___________.

Node produces _____ and ________

AVE produces ______ and Otx-1Knock-out of one of these results no

_________

The Hox genes specify _________________ polarityThese are homologous to _________ gene complex (Hom-C) of __________

Recall that the Hom-C genes are arranged in the same order as their expression pattern on anterior-posterior axis

Mammalian counterparts are clustered on____________________ .

Equivalent genes (Hoxb-4 and hoxd-4) are called a ____________ _________.

C. Anterior-posterior axis formation

Fig. 11.36- Hox genes are organized in a linear sequences that concurs with posterior to anterior structures

This is referred to as the ___________

C. Anterior-posterior axis formation (cont.)

Hoxa-3 KO- thymus, ______________ malformed

Hoxa-2 KO- _______ missing, duplicate incus

Incus

Stapes

1. Different sets of Hox genes are required for __________ of any region of the _____________________ axis

Hoxd-3 KO = deformed ______ (1st vertebra)

Hoxa-3/Hoxd-3 _______ KO- atlas and neck cartilage nearly absent

2. Different members of a paralogous group may specify different ___________ in a given region

Hox gene rules

3. A hox gene KO causes defects in the _____________ of that gene’s expression

Example

Retinoic Acid has a profound effect on development

Structure of retinoic acid (not in textbook)Fig. 10.41

Recall amphibian development (Ch. 10)

RA

Retinoic acid activates mammalian _____ genes

Wild-type mouse embryo

RA-treated mouse embryo

Lacks all distal

vertebra

Retinoic acid is likely produced in the _____, and perhaps more time

spent in the node dictates more ___________

specification

Hox geneRetinoic acid bind a receptor,

then the complex binds promoter of a hox gene

D. Dorsal-ventral axis formation

Inner cell mass (ICM)

Dorsal axis forms from ICM cells near _____________

Ventral axis forms from ICM cells near _____________

Blastocoel

Fig. 11.32

Trophoblast

E. Left-right axis formation

Note that mammals are ___________

Fig. 11.42

Two levels of regulation-1. Global- an ____ gene defect results

in all ______ on the wrong side

2. Organ-specific- an ___gene defect causes the axis of an organ to change

Organs are located in specific locations